Heater core leak

Hi Joe. It is a brand new heater core. Thanks for your quick response. After I posted my query I looked it over again, this time from under the hood at the firewall, about an hour later to calm down my frustration. I held the hoses and thought "maybe I missed something here" and lightly pulled. There was a lot of slack. I felt so stupid. The hex screw holding the pipes on the core wasn't tightened all the way and loose as a $5.00 hooker. To verify it I had my girlfriend jiggle it while I looked from inside at the core, sure enough it was really loose. The t20 hex I used was too fat to get the screw tight enough. I'll be stopping at the local Advanced Automotive shop in the morning. I hope it didn't strip the threads on the o-ring cover as it felt like it didn't want to turn anymore. The leak is at that spot too. I already replaced a bunch of electrical to get it running and replaced the power steering pump on the other rig last week. Live and learn I guess. Thanks for your input and question Joe. :)